Top PDF Experimental analysis of crack evolution in concrete by the acoustic emission technique

Experimental analysis of crack evolution in concrete by the acoustic emission technique

Experimental analysis of crack evolution in concrete by the acoustic emission technique

The AE system comprised of an eight channel AEwin system, a general-purpose interface bus (PCI-DISP4) and a PC for data storage analysis. A 2D analysis with an AEwin algorithm is performed for the localization of AE events. For the source to be located in 2D, a wave must reach at least three sensors. In this study, 4 piezoelectric sensors with a frequency of 50-200 kHz and a resonance frequency of 150 kHz were used. The transducers were placed around the expected location of the FPZ to minimize errors in the AE event localization. They were placed on the specimen with silicon grease as the coupling agent. The sensors form a rectangular grid location on one side of (75 x120 mm²) for UN200 beams, (60 x120 mm²) for UN100 beams, (105 x 120 mm²) for SN200 beams and (110 x 120 mm²) for LN200 beams [17] (Fig. 1). The detected signals were amplified with a 40 dB gain differential amplifier. The recorded AE amplitudes ranged from 0 to 100 dB. In order to overcome the background noise, the signal detection threshold was set at a value of 35 dB slightly above the background noise. The acquisition system was calibrated before each test using a pencil lead break procedure HSU-NIELSEN [18]. Location accuracy is measured in the range of 5 mm by applying the pencil lead fracture at a known location of the specimen. The measured effective velocity is equal to 3800 m/s. Each waveform was digitized and stored and signal descriptors such as rise time, counts, energy, duration, amplitude, average frequency and counts to peak were captured and calculated by AEwin system.
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Experimental Study on the Characteristics of Acoustic Emission in Damage Evolution Process of Marble under Uniaxial Compressive Load

Experimental Study on the Characteristics of Acoustic Emission in Damage Evolution Process of Marble under Uniaxial Compressive Load

In log-log coordinates n points (logW (r), log (r)) can be achieves, these points are fitting, fitting for the straight line shows that acoustic emission sequence at a given scale has fractal characteristics, the slope of the linear fitting by the absolute value of acoustic emission related parameters of the correlation dimension, namely:

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Repositório Institucional UFC: A Model for predicting damage evolution in heterogeneous viscoelastic asphaltic mixtures

Repositório Institucional UFC: A Model for predicting damage evolution in heterogeneous viscoelastic asphaltic mixtures

Investigations in asphaltic mixtures have typically not taken into account the heterogeneity of the material at the scale of the aggregate and asphaltic cement. The paper herein presents the sequel to a study that attempts to address this issue by using a micromechanics approach to investigate crack growth in asphaltic mixtures. The improvement incorporated was the consideration of the viscoelastic behavior of the bulk asphalt binder and a micromechanical viscoelastic cohesive zone model capable of accounting for both damage evolution and crack growth in viscoelastic media through the introduction of ductility at the crack tip. The numerical results were compared to experimental results obtained from the IDT test wherein monotonically increasing displacements are applied to the specimen. Although the current study has considered crack growth only under monotonically increasing loading, the technique may also be applied to fatigue loading, which is the next step in this research effort.
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Failure behavior monitoring and evaluation of steel–confined reinforced concrete columns by acoustic emission under quasi-static loading

Failure behavior monitoring and evaluation of steel–confined reinforced concrete columns by acoustic emission under quasi-static loading

The acoustic emission AE technique has been extensively studied in nondestructive testing NDT and is currently applied in civil engineering for SHM and damage evaluation. In traditional SHM and NDT methods, the generally accepted approach involves the use of gauge metrologies, in which the main challenges is related to sen- sors that are only sensitive to a local area. The extensively studied vibration-based methods can provide overall damage information, but lack sensitivity to small damages Baghiee et al., 2009 . AE is sensitive to small damages, and it not only can monitor the damage state of the sensor site, but also can monitoring certain areas where excited stress wave are readily accessible, without having to affect the integrity of structures Philippidis and Assima- kopoulou, 2008 . Given its unique superiorities, the AE technique has been a reliable routine inspection approach for civil structures, especially massive concrete, bridge girder, and cable structures where access are difficult. The present work aim at apply the AE technology to detect the damage state of steel-confined RC columns and offer new method for long-term SHM project for composite structures.
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Damage evaluation and failure mechanism analysis of steel tube confined reinforced-concrete columns by acoustic emission technology

Damage evaluation and failure mechanism analysis of steel tube confined reinforced-concrete columns by acoustic emission technology

AE energy, derived from the time integral of the square of the instantaneous signal voltage V ( t ) over the sig- nal duration, can be related to the intensity of cracks, and the accumulation of AE energy can reflect damage se- verity. Figures 5(a), 6(a) and 7(a) provide the variation of cumulative AE energy and loading history during the whole damage process. With the increase of axial load, the curve of cumulative AE energy increase continuously and the damage get further intensified. There are always a noticeable knee point of slope change in cumulative energy curve, at nearly 600 s, 800 s, and 1050 s for the three test group. The cumulative AE energy increased slowly from the initial loading period and a sharp rise occurred near the ultimate load. The slowly accumulation of AE energy implies the progressive development of structural damages, while the sharp increase of AE energy means the occurrence of some major damages, and the columns are in a unstable state.
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A Strategic Analysis of Search Engine Advertising in Web  based-commerce

A Strategic Analysis of Search Engine Advertising in Web based-commerce

This enormous success of Search Engine lies in its unique features like free access, user friendly interface, and availability of multiple Search Engines. The expertise of a Search Engine lies in its search algorithm which is a major player in fetching results for user query. India has seen the emergence of Online Business Industry as a major revenue generating Industry. This has created a race to expand business online. Google, Yahoo, MSN, have emerged as major Search Engines in India. Apart from these India has seen the emergence of local tailor made Search Engines like Khoj, Guruji, Justdial. The success of Search Advertising strategy lies in the fact that it is based on contextual advertising. Contextual advertising implies that the advertisements will be displayed relevant to the search query of the user. This increase the probability that the user will click the advertisement as it may be of its interest. Study by Anurag Gupta((2006) shows that search advertising globally is already as large as banner / display advertising. Popularity of Search Advertising lies in the fact that it is contextual and so leads to better response and secondly and more important the entire cost is based on performance (clicks) i.e. an advertiser only pays when someone clicks on his advertisement. Search Engine Marketing (SEM) has emerged as truly the marketing model of the future. With big companies like Kingfisher Airlines, MTV, Pfizer, Novartis investing in the Pay Per Click (PPC) model many Indian companies like communicate 2,web techies have came up that are totally based on Search Engine Marketing Industry.
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Acoustic Emission of a Single Bubble Activities

Acoustic Emission of a Single Bubble Activities

The bubble burst at the free surface is independent of other parameters except for bubble size and liquid viscosity. Thus the bubble burst event was taken in this experiment and statistically analysed to determine the best AE parameter indicator. Tables 3 shows the average and standard deviations for comparison between AE parameters (AE Amplitude, AE Count, AE Average Frequency, AE Absolute Energy and AE Rise Time) from sensor-3 (bubble burst). The average calculation set out in Table 3 was taken from 25 test samples. Noted here, the results are based on the raw data taken from the AE system. The result of certain AE parameters is disputed when the standard deviation has a higher than average value as shown in Table 3 (AE count, AE Average Frequency, AE Absolute Energy and AE Rise Time). This gives indication for further analysis; careful measures and consideration are needed such as background noise elimination from waveform analyse. Generally the results show the trend that the bigger the bubble size, the bigger the AE amplitude, AE Absolute Energy, AE Count and AE Rise time. In contrast, the AE Average Frequency decreases with increasing bubble size.
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Eutectic solidification as explained by the thermodynamics of irreversible processes

Eutectic solidification as explained by the thermodynamics of irreversible processes

There are some parts of the s / l interface of non-faceted phase lamellae where instability develops or vanishes and branching of faceted phase lamellae is observed. This phenomenon decides on the existence of a whole spectrum of interlamellar spacings, O . From the thermodynamic viewpoint some regions of the system are in stationary state while others in state of rotation around it. Stationary state changes continually its localization. Thus, some respective regions oscillate from rotation (marginal stability for which excess entropy production vanishes) to stationary state. This is the fundamental assumption in the current analysis.
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Analysis of Carbon Diffusion during Bainite Transformation in ADI

Analysis of Carbon Diffusion during Bainite Transformation in ADI

Suppose that the subunit denoted 1 of bainitic ferrite forms without diffusion, but any excess carbon is soon rejected into the residual austenite. Consequently, all the subunits denoted 1 were formed at the early stage of transformation from austenite whose carbon concentration is initially identical to that of bulk alloy (region of upper bainite). The subunits denoted 2 and 3 were formed from enriched austenite as a consequence of carbon redistribution occurring after the growth event (region of lower bainite). The transition between these two regions is not sharply defined. There is then the possibility of the reaction beginning with the growth of upper bainite but decomposing to lower bainite from the enriched austenite at the later stages of reaction. This explains why both upper and lower bainite sometimes can be found in the same temperature.
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CONTINUOUS CREATION IN THE PROBABILISTIC WORLD OF THE THEOLOGY OF CHANCE

CONTINUOUS CREATION IN THE PROBABILISTIC WORLD OF THE THEOLOGY OF CHANCE

The principle of divine control is very important in discussions con- cerning the relation between the Creator and His creatures. These seem to be based on two assumptions. The irst assumption is that God can achieve all His purposes in the created world (divine providence) if and only if He controls every existing being. Therefore, divine control must be perfect and unrestricted (divine volitions must be determined in every respect). Maximal possible control consists in the fact that God creates ex nihilo every being and subsequently conserves them. The second assumption is Anselmian: God is the greatest possible being one can conceive. A perfect being has everything under its control and a perfect being controls everything in the most perfect way possible. Furthermore, the best way to control everything is to create every being out of nothing and to create it as absolutely depen- dent in existence and nature upon God’s will. Omnipotence thus means to conserve continuously all created beings. Continuous creation is the best way to express divine perfection: perfect power and perfect will. Therefore, all contingent beings exist this or that way as long as divine power is acting and divine will wills itself to act upon a given being.
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Detection of coatings within liquid-filled tubes and containers by mode conversion of leaky Lamb waves

Detection of coatings within liquid-filled tubes and containers by mode conversion of leaky Lamb waves

inside a tube and a container arrangement show a clear de- pendency on coating thickness for the measured transmission times and amplitudes. For technical realization, the transmis- sion time of the residual Lamb wave is suggested, because of the minor cross sensitivity to temperature and liquid mixture. The new measurement method of coating detection within liquid-filled tubes and containers by mode conversion of leaky Lamb waves has the huge advantage of a lower detec- tion limit compared to traditional ultrasonic methods such as transmission technique or pulse–echo technique. In this pa- per it has been demonstrated that the detection range for coat- ing detection by leaky Lamb wave is from 50 to 250 µm. For traditional ultrasonic transmission technique it is from 500 to 6000 µm (Withers, 1996), and for pulse–echo technique it is from 100 to 500 µm (Withers, 1996). Moreover, the de- tection of coating by leaky Lamb wave is non-invasive. This means that the boundary of sterility is not breached, since the single-phase transducers are attached on the outer side of the tube or container wall. Other sensors with such a low detec- tion range, such as fiber optical sensors, electrochemical sen- sors, pressure sensors or heat sensors, have to be positioned inside the tube or container, causing problems with steril- ity and cleanability. In the future more work on modeling, especially adhesion conditions and material parameters, and further measurements with different tube or container wall materials and coatings ought to be done, to get calibration models and curves for technical realization.
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Continuous Modification of Cast Iron by the FLOTRET Method

Continuous Modification of Cast Iron by the FLOTRET Method

The measured values of the delay between the shedding of modification chamber and residual magnesium are dependence which is shown in Fig. 8. Length of the delay between the individual melts, respectively shedding of modification chamber by melt, has a significant influence on the temperature of the reaction chamber and thus has an influence on the resulting value of the residual magnesium. The maximum length of the delay is circa 80 minutes according to the measured values. After this time, residual magnesium guaranteeing formation of spheroidal graphite in modified cast iron decrease into sinks to the bottom line. If this delay is longer it is necessary to ensure reheating of the modification chamber by gas burner or to shed the chamber by cast iron without modification. This fact is evident from the values Mg res on Fig. 6 for the melts made on 1.7. The delay
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Assessment Of Some Acceleration Schemes In The Solution Of Systems Of Linear Equations.

Assessment Of Some Acceleration Schemes In The Solution Of Systems Of Linear Equations.

Abstract: In this paper, assessment of acceleration schemes in the solution of systems of linear equations has been studied. The iterative methods: Jacobi, Gauss-Seidel and SOR methods were incorporated into the acceleration scheme (Chebyshev extrapolation, Residual smoothing, Accelerated gradient and Richardson Extrapolation) to speed up their convergence. The Conjugate gradient methods of GMRES, BICGSTAB and QMR were also assessed. The research focused on Banded systems, Tridiagonal systems and Dense Symmetric positive definite systems of linear equations for numerical experiments. The experiments were based on the following performance criteria: convergence, number of iterations, speed of convergence and relative residual of each method. Matlab version 7.0.1 was used for the computation of the resulting algorithms. Assessment of the numerical results showed that the accelerated schemes improved the performance of Jacobi, Gauss-Seidel and SOR methods. The Chebyshev and Richardson acceleration methods converged faster than the conjugate gradient methods of GMRES, MINRES, QMR and BICGSTAB in general.
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Explicit and implicit approach of sensitivity analysis in numerical modelling of solidification

Explicit and implicit approach of sensitivity analysis in numerical modelling of solidification

Keywords: Application of Information Technology to the Foundry Industry: Solidification Process: Numerical Tcchniqucs: Sensitivity Analysis; Borzndary Elcmcnt Mcthod.. Introd[r]

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Evaluation of susceptibility of the ZRE1 alloy to hot cracking in conditions of forced strain

Evaluation of susceptibility of the ZRE1 alloy to hot cracking in conditions of forced strain

The nil strength temperature (NST) for the alloy was determined by testing cylindrical Ø 6 x 90 mm specimens on the Gleeble 3800 simulator. S-type thermocouples were pressure welded to the specimens, and then the specimens were fixed in the chamber by means of copper holders. Constant distance of 52.4 mm was kept between the holders. After evacuation of air, the chamber was filled with argon (to 0.14 hPa). Then, the 0.6 – 0.7 kN minimum pre-load was applied and was maintained until the end of experiment. The specimens were heated at the 20 o C/s rate to 400 o C, and then at the 1 o C/s rate. The NST was determined as the temperature at which the specimen lost its cohesion. The NST for the ZRE1 alloy in as-delivered state is 535 o C.
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	Field Cancerisation of the Upper Aerodigestive Tract: Screening for Second Primary Cancers of the Oesophagus in Cancer Survivors

Field Cancerisation of the Upper Aerodigestive Tract: Screening for Second Primary Cancers of the Oesophagus in Cancer Survivors

41. Wang WL et al. The beneit of pretreatment esophageal screening with image-enhanced endoscopy on the survival of patients with hypopharyngeal cancer. Oral Oncol. 2013;49(8):808-13. 42. de Monès E et al; Socéité Française de l’Otorhinolaryngologie. Initial staging of squamous cell carcinoma of the oral cavity, larynx and pharynx (excluding nasopharynx). Part 2: Remote extension assessment and exploration for secondary synchronous locations outside of the upper aerodigestive tract. 2012 SFORL guidelines. Eur Ann Otorhinolaryngol Head Neck Dis. 2013;130(2):107-12.
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The strut-and-tie models in reinforced concrete structures analysed by a numerical technique

The strut-and-tie models in reinforced concrete structures analysed by a numerical technique

1 − W j W in eq. [3] tends to zero. Thus, each term is understood to represent a vector element of the discretized structure. Tanskanem [17] also highlights the fact that the removal of an element can affect the convergence of the optimization procedure, because the criteria for withdrawal in the ESO is indicated by the attendance of inequality [1a], which can often be extreme, since there are elements that are left in the vicinity of this condition, which are numerically excluded, but they have strain energy equivalent to the structure; the gradient is thus also zero, but it should compose the gradient vector that deines the stationary point cited by Tanskanem [17]. Thus, the removal of an element drastically may unduly affect the way the optimum; one way to correct this devia- tion would be the possibility of inserting the element in the structure again. In this sense, a variant of the ESO, the BESO - Bidirectional Evolutionary Structural Optimization stands out, Querin [18]. SESO comes from this mathematically consistent philosophy, weighting the Young’s modulus (E), making the strain energy of the element in- creases, tending to the strain energy of the structure then the gradient tends to zero and the direction of the minimum is restored.
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Estudo do colapso progressivo de pórticos planos de concreto armado via análise não linear

Estudo do colapso progressivo de pórticos planos de concreto armado via análise não linear

52. OLIVEIRA, C. et al. Computational assessment of the progressive collapse of a five story structure considering two different building codes. In: THEMATIC CONFERENCE ON COMPUTATIONAL METHODS IN STRUCTURAL DYNAMICS AND EARTHQUAKE ENGINEERING, 21., 2013, Greece. Anais. Greece: Eccomas 2012, 2012. p. 325-337

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How archer fish achieve a powerful impact: hydrodynamic instability of a pulsed jet in Toxotes jaculatrix.

How archer fish achieve a powerful impact: hydrodynamic instability of a pulsed jet in Toxotes jaculatrix.

dynamics of the jet during its propagation to the prey, which proves to be essential to understand the physical mechanism that leads to a powerful impact. Therefore, in order to attain a time resolved characterization of the jet we employed a high-speed video recording technique. This non-invasive diagnostics allows us to determine the kinematics of the jet and to estimate the time evolution of the characteristic size and volume of different parts of the jet. The main requirement of the method is the availability of lateral movies of the jet, free from distortions due to the refraction at the lateral walls of the tank hosting the fish. Lateral movies are obtained by obliging fish to align parallel to a lateral window of the tank when they squirt a jet of water to prey. The alignment of fish has been obtained by placing a narrow slit on top of the water tank, so that they are able to localize the prey precisely with both eyes only when their sagittal plane is parallel to the side of the tank used as observation window [19]. A typical lateral-view image sequence of the flight (Video S1) of the jet to the prey involves an initial acceleration phase (Fig. 1A–C), followed by a nearly ballistic phase (Fig. 1D–E), and by the impact (Fig. 1F). The jet appears as being composed of a thin tail and a bulged head, with the volume of the head of the jet progressively increasing during the flight (Fig. 1G, I). In the investigated range of shooting distances (97– 153 mm), the motion of the head of the jet is compatible with a linear trajectory (Fig. 1H), independently of the shooting angle. The distribution of the elevation angle of the jet above the horizon (Fig. 1J) peaks around 74u. Data for the velocity and acceleration of the head of the jet as a function of time (Fig. 2A–B) have been obtained from the same shooting sequences of Fig.1H. The jet of water is ejected from the mouth of the fish with a typical velocity of about 2 m/s. At such small velocities the drag of the
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Stainless Steel Bonded to Concrete: An Experimental Assessment using the DIC Technique

Stainless Steel Bonded to Concrete: An Experimental Assessment using the DIC Technique

Abstract: The durability performance of stainless steel makes it an interesting alternative for the structural strengthening of reinforced concrete. Like external steel plates or fibre reinforced polymers, stainless steel can be applied using externally bonded reinforcement (EBR) or the near surface mounted (NSM) bonding techniques. In the present work, a set of single-lap shear tests were carried out using the EBR and NSM bonding techniques. The evaluation of the performance of the bonding interfaces was done with the help of the digital image correlation (DIC) technique. The tests showed that the measurements gathered with DIC should be used with caution, since there is noise in the distribution of the slips and only the slips greater than one-tenth of a millimetre were fairly well predicted. For this reason, the slips had to be smoothed out to make it easier to determine the strains in the stainless steel and the bond stress transfer between materials, which helps to determine the bond–slip relationship of the interface. Moreover, the DIC technique allowed to identify all the states developed within the interface through the load–slip responses which were also closely predicted with other monitoring devices. Considering the NSM and the EBR samples with the same bonded lengths, it can be stated that the NSM system has the best performance due to their higher strength, being observed the rupture of the stainless steel in the samples with bond lengths of 200 and 300 mm. Associated with this higher strength, the NSM specimens had an effective bond length of 168 mm which is 71.5% of that obtained for the EBR specimens (235 mm). A trapezoidal and a power functions are the proposed shapes to describe the interfacial bond–slip relationships of the NSM and EBR systems, respectively, where the maximum bond stress in the former system is 1.8 times the maximum bond stress of the latter one. Keywords: stainless steel, concrete, bond failure, digital image correlation.
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